by Scottie Westfall

A new cryptic species of gray fox?

A few weeks ago, we lost at least two canid species. Analysis of whole genome sequences indicated that the red and Eastern wolves are recent hybrids between wolves and coyotes. Indeed, this study also showed that the genetic variance between coyotes and wolves is equivalent to the variance between wolf populations, which actually calls into question whether coyotes are a valid species as well.

But this finding does not mean that there aren’t new cryptic species to be found in North America’s endemic canids.

I was just perusing some of the literature on gray foxes, when I came across this study in PLOS ONE. The authors sequenced mitochondrial DNA from 169 gray foxes from California and Georgia, as well as 11 “island foxes” and added in a sample from an aberrant gray fox that wound up in Washington State.

The authors were trying to figure out if California and the American Southeast represented a kind of “glacial refugia” for the species during the Last Glacial Maximum.

What they found was a deep divide between Eastern and Western populations. The California and Washington samples and those from the “island foxes” were estimated to have separated from the Georgia samples some 500,000 years ago. That’s actually greater than current genetic distance between Old World and North American red foxes, which separated 400,000 years ago, and are currently being proposed as distinct species.

We know from previous studies on Eastern gray fox mitochondrial DNA studies that the gray foxes of the Northeast are relatively recent colonizers from the Southeast. So my guess is that we’d find a similar divergence between gray foxes from New York and Ohio and those from California as was seen in this study with Georgia and Western gray fox samples.

Now, this study looked at only mitochondrial DNA, and this is only a tiny part of the genome. More detailed genetic studies are needed to determine the exact time of divergence between the two gray fox populations. Further, because this study included foxes from only California, Washington, and Georgia, it doesn’t really show us where the divide between these two lineages exists on the North American continent. More samples from across the range of gray foxes could give us that answer. My guess is there is a hybrid zone between the two lineages either in the Southwest or in the South-Central US.

But this assumes that there really this genetic divergence is confirmed with nuclear DNA sampling. It could be that the Western population just has an old mitochondrial DNA sequence that wound up surviving, even though the majority of the gray fox genome comes from same source as the Eastern gray fox.

It could be, but there is still a very strong possibility that Western gray foxes do represent a distinct species from the Eastern gray fox, and this question can be answered. We just need analysis from a bigger part of the genome from a broader cross section of gray foxes.

If there actually is a distinct species of Western gray fox, then it would be obvious that the island foxes, which have only been on the Channel Islands for 7,100-9,200 years, should be classified as part of that species. The authors found that no extant population of gray fox in California actually gave rise to the island fox, but there are similarities between island foxes and those in Northern California. But they were still part of this Western gray fox division.

I’ve thought it very odd that gray foxes live in Minnesota quite well, but in the West, they don’t come as far north as western Oregon. The Washington sample in this study was the first gray fox found north of the Columbia River, and western Washington has a much, much milder climate than Minnesota.

Maybe the differences in range reflect a difference between species. Maybe the gray fox of Minnesota is the same as the gray fox of Georgia, and this species has evolved more cold tolerance than the Western species.

There are just so many questions that arise from one study that has largely been overlooked.

And if there are two species of gray fox on the North American mainland, there could be several cryptic species of gray fox in Mexico and Central America. Maybe the isolated populations of gray fox in Colombia and Venezuela are also different species.

The Urocyon foxes are really interesting animals. They are the most basal of all canids, and among North American canids, they are the only one without any connection to Eurasia.

Most taxonomists divide the genus into two species: the gray fox and the island fox. The island fox was recently removed from the Endangered Species List, but I’ve always been very doubtful that it actually is a species. Most of the evidence now shows that it was actually introduced by people. Something very similar could happen with red foxes in Australia, which are now reproductively isolated from the rest of the Old World red foxes. Maybe in 9,000, they will be morphologically distinct enough for someone to declare them the “Australian fox” and work to preserve them as a distinct species.

But in focusing so much on this odd insular population, could we have missed the really big story about the urocyon? Maybe there were two species after all, but we never bothered to look into it.

Maybe one day, we’ll have Urocyon cinereoargenteus and Urocyon occidentalis as the two species of gray fox native to the United States.

2 Responses

Old World and North American red foxes had originally been thought to be discrete species until about the middle of the 20th century when the taxonomic lumpers had their way and decided the two populations belong to a single species. There is nothing new in the idea that red fox populations of the old and new world are distinct enough to warrant being classified as separate species.

I guess nobody has tried crossbreeding eastern and western gray foxes? That there should be two genetically distinct populations of gray fox isn’t a surprise. They have a hard enough time crossing the Columbia river let alone making regular crossings of the Mississippi.